Polymer encapsulated ceramic superconductors

ABSTRACT

The invention features a superconducting ceramic conductor for use in a preselected fluid cryogen. The conductor includes a composite ceramic superconducting wire having an outer surface along its length and a sealing structure hermetically surrounding the outer surface to prevent the cryogen from infiltrating into the wire and degrading its superconducting properties. The sealing. structure includes a cured polymer layer encircling the outside surface of the wire.

CROSS-REFERENCE TO RELATED APPLICATIONS

The application is a continuation-in-part of parent application U.S.Ser. No. 09/360,318 filed Jul. 23, 1999 entitled “Encapsulated CeramicSuperconductors.” The parent application is incorporated herein byreference.

BACKGROUND OF THE INVENTION

The invention relates to composite ceramic superconducting tapes andstructures. Tapes including ceramics such as YBa₂Cu₃O_(7-δ) (YBCO 123),(Pb,Bi)₂Sr₂Ca₂Cu₃O (BSCCO 2223), and (Pb,Bi)₂Sr₂Ca₁Cu₂O (BSCCO 2212) canbecome superconducting at relatively high temperatures, e.g., liquidnitrogen temperatures, and are ideal for carrying electrical currentover large distances. The composite superconducting tape usuallyincludes superconducting portions of ceramic material within aconductive metal matrix (e.g., BSCCO filaments within a noble metalmatrix) or superconducting portions coated on a conductor (e.g., one ormore layers of YBCO or BSCCO supported on a conducting substrate). Asupport structure such as a metallic tape can be laminated to thecomposite superconducting tape to provide it with mechanical strengthand resilience. During operation the superconducting article (e.g.,superconducting tape and support structure) is immersed in fluid cryogen(e.g., liquid nitrogen, liquid helium, or supercritical helium) for anextended period of time. During this time fluid cryogen may infiltrateinto the superconducting ceramic material. For example, the infiltrationmay occur when a portion of the ceramic material, which can be porous,is directly exposed to the cryogen, or when one or more surface defectsin the composite material provide a channel between the cryogen and theceramic material.

Such infiltration can be a serious problem because upon warming thearticle, the cryogen can quickly vaporize, causing pressure to build upwithin the article. For example, the density of liquid nitrogen at 77 Kis seven hundred times greater than that of nitrogen gas at ambientconditions. The pressure build up within the article can create a largephysical defect in the superconducting ceramic and significantly degradeits superconducting properties (e.g., transport properties), thusblocking the desired electrical performance of the article. Because thedefect introduces the appearance of a bulge or balloon on the exteriorof the superconducting article, this problem is referred to as the“balloon” problem.

SUMMARY OF THE INVENTION

Applicants have discovered that even where composite ceramicsuperconducting tapes have a metal coating applied to their surface,cryogen may still infiltrate into the ceramic material through porous ormicroporous defects in the coating and form balloons. Such defects canbe difficult to locate prior to balloon formation because they can beexceedingly small and rare along the length of the tape. Thus, a coatedtape vulnerable to balloon formation may, to the eye, look perfect priorto cryogenic thermal cycling. Moreover, the likelihood of cryogeninfiltration through such defects increases when the fluid cryogen isunder pressurized conditions, e.g., up to about 1 to 33 bars, and whenthe superconducting article is exposed to the fluid cryogen for longperiods of time, e.g., several weeks, several years, or many years. Suchconditions are typical for superconductive cabling applications.

Applicants have recognized that a surface defect in the compositeceramic superconducting tape can cause an overlapping defect in anapplied metal coating. For example, a surface defect may prevent solderfrom wetting over the defect, thereby causing a microporous defect toform in an applied solder coating. The overlapping defects can provide achannel through which cryogen can infiltrate into the ceramic material.In tapes formed of BSSCO filaments in a noble metal matrix, for example,such surface defects can result from oxides released from the BSSCOpowder during the powder-in-tube fabrication of the composite ceramictape.

More generally, defects in the composite ceramic tape and metal coatingcan result during handling and applications manufacturing. Microporousdefects in the metal coating can also be caused by shrinkage voidsduring cooling of the metal coating when the corresponding dimensions ofthe metal coating are too large (e.g., larger than 0.080″).Statistically, some defects in the composite ceramic tape may overlapwith defects in the metal coating to form one or more channels throughwhich cryogen can infiltrate into the ceramic material.

Embodiments of the present invention substantially prevent such cryogeninfiltration by completely encapsulating the superconducting tape alongits length within a sealing structure. The sealing structurehermetically seals the entire surface along the length of thesuperconducting tape (e.g., the top, bottom, and sides of the tape) fromthe cryogen bath to prevent cryogen infiltration. For example, in oneembodiment, a first stainless steel tape is laminated to the top of thecomposite ceramic tape and a second stainless steel tape is laminated tothe bottom of the composite ceramic tape to sandwich the compositeceramic tape. The stainless steel tapes are selected to be wider thanthe composite ceramic tape so that they overhang the sides of thecomposite ceramic tape. Solder fillets can then seal the sides of theceramic tape because the solder can wet to the overhanging portions ofthe metallic tapes and form a continuous surface covering the sides ofthe composite ceramic tape. The combination of the metallic tapes andthe solder fillets thus forms the sealing structure.

The sealing structure can generally provide mechanical reinforcement tothe composite ceramic tape, e.g., by including one or more metalliclaminates. Alternatively, the sealing structure can be separate fromsuch support structure, e.g., it can encapsulate a ceramic tape alreadyhaving one or more metallic laminates bonded thereto for providingmechanical reinforcement.

In general, in one aspect, the invention features a superconductingceramic conductor for use in a preselected fluid cryogen including: acomposite ceramic superconducting; wire having an outer surface alongits length; and a sealing structure hermetically surrounding the outersurface to prevent the cryogen from infiltrating into the wire anddegrading its superconducting properties.

The superconductor can include any of the following features. The wireand surrounding sealing structure can be greater than 50 meters long.The wire can include a metallic matrix supporting a plurality ofsuperconducting ceramic filaments. Alternatively, the wire can includeat least one superconducting ceramic layer and at least one metallicsubstrate supporting the at least one superconducting ceramic layer. Thesealing structure can be metallic. The sealing structure can prevent thecryogen from infiltrating into the wire through the outer surface underpressurized conditions, for example, the pressurized conditions canexceed about 10 atm and the fluid cryogen can be liquid nitrogen.

Furthermore, the wire can be a composite ceramic superconducting tapehaving a top face, a bottom face, and side faces, and wherein the outersurface is the top, bottom, and side faces. For example, the sealingstructure can include: a first metallic tape laminated to the top faceof the composite tape; a second metallic tape laminated to the bottomface of the composite tape, the first and second metallic tapesextending beyond the side faces of the composite tape; and non-poroussolder fillets adjacent the side faces of the composite tape fillingspace between the metallic tapes. The metallic tapes can includestainless steel, Cu—Be alloy, aluminum, copper, nickel, or Cu—Ni alloy.The first and second metallic tapes can be at least 5% wider than thecomposite tape to extend beyond the side faces of the composite tape.The composite tape and the sealing structure can define an aspect ratiofor the conductor that is greater than about five. Alternatively, thesealing structure can include: a first metallic tape laminated to thetop face of the composite tape and having portions extending beyond theside faces of the composite tape; and a second metallic tape laminatedto the bottom face of the composite tape and having portions extendingbeyond the side faces of the composite tape, wherein adjacent each sideface the extended portion of the first metallic tape is welded to theextended portion of the second metallic tape.

In other embodiments, the sealing structure can include a ductilemetallic sheet encircling the outer surface of the wire, wherein regionson opposite sides of the metallic sheet are welded to one another.Alternatively, the sealing structure can be a cured polymer layerencircling the outside surface of the wire. In either case, theconductor can further include a metallic tape laminated to the wire formechanical reinforcement with the ductile metallic sheet or curedpolymer layer encircling the wire and the metallic tape. The curedpolymer layer can include conductive media, e.g., metallic elementsdispersed within the polymer layer. Where the wire has a substantiallyrectangular cross section, the conductive media can permit the polymerlayer to be conductive at least along a direction parallel to thethickness of the wire.

In another aspect, the inventions features a superconducting cableincluding the superconducting ceramic conductor described above.

In a further aspect, the invention features a superconducting coilincluding the superconducting ceramic conductor described above.

In a further aspect, the invention features a cryogenically cooledassembly including: a vessel for containing a fluid cryogen; a fluidcryogen; and a superconducting article at least partially immersed inthe fluid cryogen, the article including the superconducting ceramicconductor described above in direct contact with the fluid cryogen. Insome embodiments, the assembly can further include a refrigeration unitfor cooling the fluid cryogen and a circulating pump for passing cryogenthrough the refrigeration unit. During operation, the circulating pumpcan cause the pressure of the cryogen fluid in the vessel to exceed 1atm or even exceed 10 atm.

In general, in another aspect, the invention features a superconductingconductor for use in a preselected fluid cryogen. The conductorincludes: a composite superconducting wire having an outer surfacesurrounding the wire along its length; and a sealing structurehermetically surrounding the outer surface to permit the superconductingceramic conductor to withstand thermal cycling in which the fluidcryogen is under pressurized conditions without degrading the currentcarrying capability of the superconducting ceramic tape by more than10%. For example, the pressurized conditions can exceed about 2 bar(e.g., in the range of about 10 to 33 bar) and the fluid cryogen can beliquid nitrogen.

In general, in another aspect, the invention features a method of makinga superconducting conductor for use in a preselected fluid cryogen. Themethod includes: providing a composite ceramic superconducting wirehaving an outer surface along its length; and hermetically surroundingthe outer surface with a sealing structure to prevent the cryogen frominfiltrating into the wire and degrading its superconducting properties.

Embodiments of the method can include any of the following features. Theprovided wire can be formed by at least one sequence of a mechanicaldeformation and a subsequent heat treatement of a container includingsuperconducting ceramic precursor. The hermetically surrounding step caninclude laminating metallic tapes to the wire, encircling at least onemetallic sheet around the outer surface of the wire, welding a pluralityof metallic sheets to one another to encircle the outer surface of thewire, or forming a polymer coating completely covering the outer surfaceof the wire. In the latter embodiment, the method can further includeadding conductive media to the polymer coating prior to covering theouter surface of the wire.

As used herein, a composite ceramic superconducting wire includes ametallic matrix supporting superconducting ceramic portions, or one ormore metallic substrates supporting superconducting ceramic portions.The composite superconducting wire can have an arbitrary cross sectionalprofile, e.g., a circular, elliptical, or substantially rectangularprofile. For example, the composite ceramic superconducting wire can bea composite ceramic superconducting tape.

For the purpose of the present invention, a superconducting wire or tapeis meant to describe an elongate composite element capable of carryingcurrent under superconducting conditions, which, after being in contactwith cryogenic fluid at superconducting temperatures for a predeterminedperiod of time and subsequently heated to a higher temperature (e.g.,room temperature), can show degradation. Such degradation is typicallyassociated with the presence or formation of one or more balloons and/orincludes a reduction of the superconducting properties, such as areduction of the transport critical current.

By way of example, a tape or wire made through a thermo-mechanicalprocess may include a metallic layer on its outer surface, withsuperconducting ceramic portions formed on the inside. Thethermo-mechanical process is capable of causing or facilitating theformation of defects that result in cryogen infiltration and subsequentdegradation of the tape or wire.

In another example, a tape or wire includes a layer of superconductingceramic material applied over a substrate and a surrounding protectionlayer, typically applied by a sputtering or vaccuum depositiontechnique. The protection layer, even if effective to protect thesuperconducting ceramic material from chemical contact with the externalatmosphere, has a thickness and strength not sufficient to prevent thecryogenic fluid penetration and the subsequent degradation it causes,particularly when exposed to the cryogenic fluid for a long time or athigh pressure.

As described above, the composite ceramic superconducting wire caninclude a metallic matrix supporting a plurality of superconductingceramic filaments extending along the length of the superconductingwire. Such a wire can be made by the well-known powder-in-tube process,which involves subjecting a container (e.g., a tube) filled withsuperconducting ceramic precursor powder to one or more repetitions of amechanical deformation and heat treatment. Such processing steps cancause defects in the metallic matrix that give rise to cryogeninfiltration. Preferably, the sealing structure is formed around thecomposite ceramic superconducting wire after the wire is madesuperconducting by the processing steps to avoid exposing the sealingstructure to the harsh processing conditions.

Preferably, the metallic matrix is formed from a noble metal. A noblemetal is a metal whose reaction products are thermodynamically unstableunder the reaction conditions employed relative to the desiredsuperconducting ceramic, or which does not react with thesuperconducting ceramic or its precursors under the conditions ofmanufacture of the composite. The noble metal may be a metal differentfrom the metallic elements of the desired superconducting ceramic, suchas silver, oxide dispersion strengthened (ODS) silver, a silver alloy ora silver/gold alloy, but it may also be a stoichiometric excess of oneof the metallic elements of the desired superconducting ceramic, such ascopper.

In another example, the composite ceramic superconducting wire is amultilayer structure including one or more layers of superconductingceramic, one or more layers of buffer or protection layers, and one ormore metal substrate layers supporting the other layers. The multilayerstructure can be formed by well-known epitaxy techniques (e.g.,sputtering, vacuum deposition, or molecular beam) Although the purposeof the buffer layers is to prevent chemical reactions between thesuperconducting ceramic and the external environment, such buffer layersare not generally sufficient to prevent cryogen infiltration,particularly when they are exposed to a fluid cryogen for a long time orat high pressure. The sealing structure is formed around the multilayerstructure to prevent the cryogen infiltration.

As used herein, “thermal cycling” involves one or more repetitions ofthree phases in which the superconducting conductor or article is soakedin a coolant bath and returned to room temperature. The three phasesare: i) a cooling phase in which the conductor or article is surroundedwith coolant, and, optionally, pressure is increased or decreased; ii) alow temperature phase at constant pressure; and iii) a warming phase inwhich the coolant is removed and, if necessary, pressure is returned toambient conditions.

Cryogen infiltration of the ceramic material can be determined byinspecting the superconducting conductor or article for balloons afterthermal cycling. As used herein, a balloon is a local increase of thecomposite ceramic wire or tape volume due to internal structureexpansion following thermal cycling. Typically, the volume increasecorresponds to a local increase in thickness, e.g., an increase of a fewpercent to greater than 100% of the total thickness. For example, aballoon can increase the thickness by,about 100%. The length of theballoon is a function of the amount cryogen penetration and longitudinalgas diffusion. Balloons have been observed to be about a few millimetersto a few centimeters long, and even longer.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which the invention belongs. All publications, patentapplications, patents, and other references mentioned herein areincorporated by reference in their entirety. In case of conflict, thepresent specification, including definitions, will control. In addition,the materials, methods, and examples are illustrative only and notintended to be limiting.

Embodiments of the invention can include many advantages. The sealingstructure can prevent cryogen infiltration through surface defects orexposed ceramic surfaces that could otherwise form “balloons” anddegrade the critical current carrying capacity of the superconductingwire during the thermal cycling necessary for its normal operation.Prevention of cryogen infiltration through defects in thesuperconducting composite ceramic wire is crucial to the longevity ofthe superconducting conductor or article. Formation of even one ballooncan end the usefulness of the superconducting conductor or article, forexample, because the balloon creates an even larger defect through whichcryogen can infiltrate and produce additional balloons upon furtherthermal cycling. This in turn further reduces the critical current ofthe superconducting wire. Because of the sealing structure, theconductor can withstand thermal cycling, even in which the fluid cryogenis under pressurized conditions, without degrading the current carryingcapability of the superconducting ceramic tape by more than 10% or evenless. Prevention of such balloons also preserves the dimensionaltolerances of the conductor.

The sealing structure can also prevent cryogen infiltration when thesuperconductive article is immersed in the fluid cryogen in apressurized environment (e.g., greater than 1 bar to about 33 bar, suchas about 10-15 bar) for long periods of time (e.g., several hours,several weeks, several years, or many years). Such conditions aretypical for cabling applications. Moreover, the encapsulation of thecomposite ceramic superconducting tape provided by the sealing structurecan be sufficiently rugged to allow the conductor to be bent or woundinto coils or a helix. Furthermore, many embodiments of thesuperconducting conductor are formed by a continuous process, whichallows the formation of long conductors (e.g., longer than about 50 m,and often longer than about several hundred meters).

Other features and advantages of the invention will be apparent from thefollowing detailed description and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a and 1 b are cross sectional diagrams of a laminatedsuperconducting ceramic conductor (FIG. 1a) and of an alternativeembodiment of the ceramic composite tape (FIG. 1b) in the conductor ofFIG. 1a;

FIG. 2 is a schematic surface view of a laminating assembly inaccordance with the invention;

FIG. 3 is a top sectional view of an inert gas (e.g., nitrogen)enclosure of the laminating assembly of FIG. 2;

FIG. 4 is a cross section of an additional embodiment of asuperconducting ceramic conductor;

FIGS. 5a, 5 b, and 5 c are cross sections of embodiments of asuperconducting ceramic conductor in which a ductile sheet is wrappedaround the ceramic tape to prevent cryogen infiltration;

FIG. 6 is a cross section of an embodiment of a superconducting ceramicconductor in which a conductive polymer layer seals the ceramic tape toprevent cryogen infiltration;

FIG. 7 is a schematic diagram of an apparatus for forming the polymerlayer in the superconducting ceramic conductor of FIG. 6.

FIGS. 8a and 8 b are schematic cross sections of embodiments of asuperconducting ceramic conductor in which metallic tape laminates arewelded to one another to seal the composite ceramic tape.

FIG. 9 is a schematic cross section of a fluid cryogen cooled assemblyincluding a superconducting article in accordance with one embodiment ofthe invention.

DETAILED DESCRIPTION

One embodiment of the invention is shown in FIG. 1a, which is a cross,sectional view of a superconducting conductor 10 immersed in a fluidcryogen bath 30, which may be pressurized for an extended period oftime. Conductor 10 includes a composite ceramic superconducting tape 12,solder layers 14 a and 14 b, metallic tapes 16 a and 16 b, and solderfillets 18 a and 18 b. Solder layers 14 a and 14 b bond metallic tapes16 a and 16 b to the top and bottom surfaces 20 a and 20 b,respectively, of composite ceramic tape 12, to thereby seal the top andbottom surfaces 20 a and 20 b from the fluid cryogen 30. As illustrated,metallic tapes 16 a and 16 b are wider than composite ceramic tape 12and overhang its sides 22 a and 22 b. Solder fillets 18 a and 18 b fillthe spaces between the overhanging portions of the metallic tapes 16 aand 16 b to thereby seal the sides 22 a and 22 b of composite ceramictape 12 from the fluid cryogen 30. The metallic tapes 16 a and 16 bprovide mechanical support to the composite ceramic tape 12 and thecombination of the metallic tapes 16 a and 16 b and solder fillets 18 aand 18 b forms a sealing structure that totally encapsulates compositeceramic tape 12 along its length to substantially prevent cryogen 30infiltration.

The composite ceramic tape 12 can include any superconducting ceramics,including superconducting copper oxides of the bismuth, rare earth,thallium, lead, or mercury families;. Typical superconducting ceramicmaterials include, for example, (Pb,Bi)₂Sr₂Ca₂Cu₃O (BSCCO 2223),(Pb,Bi)₂Sr₁Ca₁Cu₂O (BSCCO 2112), Y₁Ba₂Cu₃O_(7-δ) (YBCO 123), and rareearth metal substitutions of Yttrium in YBCO. Composite ceramic tape 12can be made using well-known processes such as powder-in-tube and coatedconductor. For a description of such processes, see for example U.S.Pat. No. 5,801,124, “Laminated Superconducting Ceramic CompositeConductors”, by Bruce R. Gamble, Gilbert N. Riley, Jr., John D.Scudiere, Michael D. Manlief, David M. Buzcek, and Gregory L Snitchler,issued Sep. 1, 1998, the contents of which are incorporated herein byreference.

Referring to FIG. 1a, composite ceramic tape 12 comprises a matrix 40 ofnoble metal surrounding and supporting a plurality of superconductingceramic filaments 42 extending substantially along the length ofconductor 10. A “noble metal” is a metal whose reaction products arethermodynamically unstable under the reaction conditions employed toprepare the ceramic tape. Thus, the noble metal matrix 40 does not reactwith the ceramic filaments 42 or its precursors during preparation ofthe composite ceramic tape 12. Suitable noble metals include, forexample, silver, oxide dispersion strengthened (ODS) silver, a silveralloy, or a silver/gold alloy. Exemplary composite ceramic tapesincluding ODS silver can be formed in accordance with U.S. Ser. No.08/731,302, “Improved Performance of Oxide Dispersion StrengthenedSuperconducting Composites” by Lawrence J. Masur et al., filed Oct. 15,1996 and corresponding European Patent Application EP 0837512, publishedApr. 22, 1998, the entire contents of both applications beingincorporated herein by reference. The metallic tapes 16 a and 16 b canbe, e.g., stainless steel, copper, copper alloy and super alloys. Thesolder 14 a, 14 b, 18 a, and 18 b is typically metallic, but canalternatively include wetted dispersions of metallic fibers or particlesin an epoxy.

Suitable dimensions for one embodiment of the conductor 10 include:composite ceramic tape 12 thickness T₁ of about 0.008″; metallic tape 16a and 16 b with a thickness T₂ of about 0.0015″; composite ceramic tape12 with a width W₁ of about 0.160″; and metallic tape 16 a and 16 b witha width W₂ of about 0.190″. Using this set of dimensions, the metallictapes 16 a and 16 b overhang each side 22 a and 22 b of the compositeceramic tape 12 by about 0.015″.

More generally, in other embodiments, W₂ can be at least 5% wider thanW₁ and up to about 30% wider; preferably W₂ is about 15% to 25% widerthan W₁. Also, composite ceramic tape 12 can have a width of about0.02-1.0″ or larger, and a thickness of about 0.001-0.040″ or larger.Metallic tapes 16 a and 16 b typically have a thickness of about0.001-0.003″ or larger, although thinner ones may be used. Thicklaminates, greater than about 0.004-0.02″, preferably about 0.006″, mayadvantageously be used in high field magnet applications. As indicatedby the dimensions above, conductor 10 tends to be more wide than thick,with an aspect ratio typically greater than about 5, e.g., an aspectratio of about 10. The solder thickness is typically in the range ofabout 0.0001″ to about 0.001″, and preferably 0.0002″ and 0.0006″. Theconductor 10 is typically hundreds of meters long. The ends (not shown)of tape 12 can also be encapsulated, e.g., by solder or silicone. Forexample, a suitable silicone sealant is Dow Corning 732 multi-purposesealant available from Dow Corning Corporation (Midland, Mich.).

Metallic tapes 16 a and 16 b are preferably selected to provide thermaland electrical conductivity, to permit cooling of the superconductingarticle, and to allow current transfer between the superconductingconductors in the article. The metallic tapes can also be selected basedon their thermal stability properties. The laminates are preferablystainless steel tapes (other metal tapes, for example, copper, copperalloy or superalloy tapes can also be suitable). The metallic tapes arealso preferably selected to have a coefficient of thermal expansiongreater than that of the superconducting ceramic tape to impartcompressive strain between metallic tapes 16 a and 16 b and compositeceramic tape 12 caused by cooling after lamination, which enhances themechanical performance of the composite. Preferably, the metallic tapeshould also be selected to have a yield strength of at least 700 MPa.

Cryogen 30 can be any cryogen capable of maintaining superconductor 10at or below its transition temperature. While not to be construed aslimiting, liquid nitrogen is the particularly preferred cryogen,suitable for use in accordance with the invention. Depending on theapplication, cryogen 30 can also be pressurized. Refrigeration performedby liquid coolants is limited by the fluid critical point at the maximumachievable pressure. For example, for liquid nitrogen, a typical valuefor pressure is in the range of about 1 to 33 bar. Furthermore, in someembodiments, refrigeration can take place at subatmospheric pressures toaffect the boiling temperature of the fluid cryogen.

The metallic tapes are laminated onto the composite tape after thecomposite tape has been formed, i.e., after the composite tape has beenmade superconducting. As a result, the sealing structure formed by themetallic tapes and solder fillets are not subject to harsh mechanicaland thermal treatments used to form composite tape 12. Such treatmentscould degrade the hermetic sealing properties of the sealing structure.

Referring to FIGS. 2 and 3, a laminator 100 forms conductor 10 bypassing composite ceramic tape 12 and metallic tape 16 a and 16 bthrough a solder wave bath 118 and pressing them together in a die.Because metallic tapes 16 a and 16 b overhang the sides 22 a and 22 b ofcomposite ceramic tape 12, capillary action adheres solder to the sides22 a and 22 b of composite ceramic tape 12 to form solder fillets 18 aand 18 b.

Laminating assembly 100 includes cleaning devices 174, 176, and 178,laminator 118, for example, a solder wave or solder bath, and a seriesof feed guides 120, 120 a, 122, 124, and 126 for guiding compositeceramic tape 12 and metallic tapes 16 a and 16 b into laminator 118. Thecleaning devices 174, 176, and 178 may be, for example ultrasoniccleaning stations, flux stations, chemical deoxidation devices ormechanical scrubbers. Conductor tape 10 preferably travels along asubstantially straight laminate process path (arrow 119) to preventdegradation of the superconductor tape 10 as it is fed through the feedguides 120, 120 a, 122, 124, and 126, the cleaning devices 174, 176, and178, and the laminator 118. Laminating assembly 100 also includes aninstrument panel 127 for input of user commands and display of systemstatus.

Composite ceramic tape 12, prior to lamination, is stored on a payoffroll 128. Metallic tapes 16 a and 16 b, prior to lamination, are storedon payoff rolls 130 and 132, respectively. A take-up roll 134 on whichthe resulting laminated superconductor tape 10 is taken-up is driven bya motor 135 and pulls composite ceramic tape 12 and metallic tapes 16 aand 16 b through the feed guides 120, 120 a, 122, 124, and 126 andlaminator 118. Payoff rolls 128, 130, and 132 preferably include brakes129, 131, and 133, respectively, for independently controlling thetension in composite ceramic tape 12 and metallic tapes 16 a and 16 b.The radius of curvature of composite ceramic tape 12 as it is fed frompayoff roll 128 is maintained at greater than about 8″ to 10″ inches toprevent mechanical, and hence electrical, degradation of thesuperconductor tape 10. Metallic tapes 16 a and 16 b can be tensionedduring the laminating process, as taught, for example, in U.S. Ser. No.08/705,811, entitled “Laminated Superconducting Ceramic Tape”, by JohnD. Scudiere, David M. Buczek, Gregory L. Snitchler and Paul J. DiPietro, filed Aug. 30, 1996, and the corresponding PCT InternationalPublication No. WO 98/09295, the entire contents of both documents beingincorporated herein by reference.

Laminating assembly 100 can include, for example, a nitrogen gasenclosure 140 housing laminator 118, a fluxer 142 located upstream oflaminator 118, and a dryer/heater 144 located between fluxer 142 andlaminator 118 to expand the composite ceramic tape 12 and the metallictapes 16 a and 16 b. Preferably, the laminator 118 includes a solderwave and associated process settings (e.g., preheat temperature,pressure, and cooling rate) to minimize voids in the solder. Processparameters and equipment settings during the soldering process enablethe formation of full fillets 18 a and 18 b on the edges 22 a and 22 bof composite ceramic tape 12 by capillary action. For example, device130 a controls the pressure on the wipe assembly.

Continuous fillets can be obtained by controlling the flux applicationand specific gravity (e.g., less than 1), the preheat temperature (e.g.,greater than 100° C.), maintaining the alignment of the tapes in thewave, applying about 2 to 5 pounds of positive pressure on the conductoras it exits the wave, and rapidly and uniformly cooling the solder(e.g., less than about 0.5 sec). Typically line speeds can be up toabout 10 m/min. Therefore, the superconducting conductors aremanufactured in a continuous fashion, permitting the manufacture ofconductors having a length of at least about 50 m, and typically muchlonger.

Solder fillets 18 a and 18 b hermetically seal sides 22 a and 22 b,respectively, of composite ceramic tape 12 because even if the solderfillets do not completely wet to sides 22 a and 22 b, they wet to theadjacent overhanging edges of metallic tapes 16 a and 16 b. As a result,each solder fillet forms a continuous surface between metallic tapes 16a and 16 b, thereby hermetically sealing the sides of the compositeceramic tape. Moreover, because the solder fillets have relatively smalldimensions (e.g., smaller than about 0.080″) along the cross section ofthe conductor, shrinkage voids do not usually occur. See, e.g.,Principles of Soldering and Brazing, eds. Humpston and Jacobson, Chapter4, section 4.4.1.2, pg. 127 (ASM International 1996). Thus, the solderfillets are non-porous and prevent cryogen infiltration into the sidesthe composite ceramic tape.

A guide dam 154 is used to control the thickness of the solder layers 14a and 14 b between metallic tapes 16a and 16 b and composite ceramictape 12. A cooler 156 blows air at, for example, less than 100° C., toremove excess solder from laminated conductor tape 10 and cools thelaminated conductor tape 10 to freeze the solder layers 14 a and 14 band solder fillets 18 a and 18 b. An additional feed guide 157 islocated downstream of cooler 156.

Located downstream of cooler 156 and feed guide 157 are a clean station190 which sprays a cleaning fluid, for example, distilled water at about70° C., over conductor 10, and a dryer 192,located downstream of cleanstation 190 including air jets at about 100° C. Guide rollers 194 and198 are located downstream of dryer 192.

Surfaces 20 a, 20 b, 22 a and 22 b of composite ceramic tape 12 arevulnerable surfaces that can have porous, defects subject to cryogenicinfiltration. Preferably, metallic tapes 16 a and 16 b are cleaned bythe same process and to the same degree. Then, tape 12 and metallictapes 16 a and 16 b are heated to a soldering temperature. The solderflux may be applied by a flux soak, spray or dip, a flux wipe, or abubbler to insure that the vulnerable surface is continuously coveredwith flux. Fluxes which do not have adverse chemical reactions with thesuperconducting ceramic or the matrix, which are cleaned in water andwhich provide maximum wetability of the tape and laminate are preferred.For example, fluxes 856, 857 and 260HF from Alpha Metals (Jersey City,N.J.) may be used. Preferred solders include Pb—Sn—Ag, Pb—Sn, Sn—Ag, andIn—Pb. Preferably, solders should have thermal and mechanical (e.g.,tensile strength, coefficient of thermal expansion (CTE), and elongationat both room temperature and cryogenic operating temperature) compatiblewith those of the laminated structure.

Tension on composite ceramic tape 12 is preferably maintained atrelatively low levels during lamination, preferably corresponding to astrain of about 0.01% or less, to prevent tape degradation. Theindependently controlled brakes 129, 131, and 133 permit the metallictapes 16 a and 16 b to be tensioned at a higher tension than compositeceramic tape 12 if desired during the lamination process. As thelaminated conductor tape 10 is cooled, the composite ceramic tape 12 andmetallic tapes 16 a and 16 b retract as they start to cool and thesolder in solder layers 14 a and 14 b and fillets 18 a and 18 b freezes,sealing the composite ceramic tape 12 to the metallic tapes 16 a and 16b.

In other embodiments, the composite ceramic tape 12 in conductor 10,which includes superconducting ceramic filaments 42 in a metallic matrix40, can be replaced with a composite ceramic tape in a coated conductorconfiguration, as exemplified by composite ceramic tape 12′ shown inFIG. 1b. Tape 12′ includes a pair of superconducting layers 45 a and 45b (e.g., YBCO (YBCO 123), rare earth metal substitutions of Yttrium inYBCO, BSSCO, or thallium-based superconductors), wherein layers 45 a and45 b each include a cap layer 43 a and 43 b, respectively. Cap layers 43a and 43 b are soldered, glued, or otherwise 10 bonded to one another(e.g., by diffusion bonded) as represented by reference numeral 44. Tape12′ further includes buffer layers 47 a and 47 b sandwichingsuperconducting layers 45 a and 45 b, and substrate layers 49 a and 49 bsupporting the buffered superconducting layers. A suitable cap layer canbe made from, for example, a conductive metal, e.g., silver, copper,aluminum, or combinations or alloys thereof. Suitable buffer layersinclude, e.g., CeO₂, YSZ (yttria stabilized zirconia), SrTiO₃, and Y₂O₃.Suitable substrate layers can include, for example, a non-ferromagneticlayer such as nickel/copper alloys. Substrate layers are described in,for example, U.S. Ser. No. 08/943,047 “Substrate with Improved OxidationResistance” by Cornelis Leo Hans Thieme, Elliot D. Thompson, Leslie G.Fritzemeier, Robert D. Cameron, and Edward J. Siegal, filed Oct. 1,1997, and corresponding PCT International Publication No. WO 99/17307published Apr. 8, 1999, the entire contents of both being incorporatedherein by reference. As described above, tape 12′ can replace tape 12 inFIG. 1a, with the structure hermetically sealing composite ceramic tape12′ (i.e., the metallic tapes and solder fillets) and its formationbeing the same as that described with reference to FIG. 1a

Alternatively, tape 12′ can be modified to be effective against cryogeninfiltration. For example, substrates 49 a and 49 b are used similarlyto the laminated metallic tapes 16 a and 16 b shown in FIG. 1a and sides22 a and 22 b are sealed from the environment as described herein (e.g.,by solder or welding).

Referring to FIG. 4, multiple stacks of the superconducting compositeceramic tapes (e.g., stacks of tape 12, or stacks of tape 12′) can belaminated between metallic tapes 16 a and 16 b by solder 14 to formconfiguration 200. As in the embodiment of FIG. 1, solder fillets 18 aand 18 b seal the sides of the tapes 12 and form because the edges ofmetallic tapes 16 a and 16 b overhang the sides of tapes 12 that wouldotherwise be exposed to cryogen infiltration.

In other embodiments, metallic tapes 16 a and 16 b can be welded, ratherthan soldered, to the top and bottom surfaces 20 a and 20 b of thecomposite ceramic tape 12 and to each other at, welding joints 99, asshown for example in FIGS. 8a and 8 b. The welded metallic tapes 16 aand 16 b completely cover and thereby hermetically seal the top, bottomand side surfaces of the composite ceramic tape 12 from the fluidcryogen 30.

In further embodiments, the sealing structure can include one or moresheets of non-porous ductile material, e.g., sheets of copper, that arewrapped around the composite ceramic tape and welded to one another tohermetically seal the top, bottom, and sides of the composite ceramictape from the fluid cryogen. Referring to FIG. 5a, for example, a crosssection of conductor 60 is shown. Conductor 60 includes asuperconducting composite ceramic tape 62 having a metallic tape 66laminated to top surface 70 a by solder layer 64. Composite ceramic tape62 and laminated metallic tape 66 are similar to those described above.Metallic tape 66 imparts mechanical strength to composite ceramic tape62. A sheet 75 of ductile material forms a sealing structure thatencircles the top, bottom, and sides of tape 62 and metallic tape 66 andextends along their length. Portions 77 and 79 on opposite faces ofsheet 75 are welded to one to hermetically seal the composite ceramictape from cryogen bath 80.

In other embodiments, multiple sheets of ductile material can be weldedto one another to encircle the top bottom and sides of the laminatedceramic and metallic tapes. Furthermore, in other embodiments a secondmetallic tape can be laminated to the bottom side 70 b of compositeceramic tape 62 to impart additional mechanical strength. Alternatively,in other embodiments, the sealing structure formed by sheet 75 impartssufficient mechanical strength to obviate the need for any laminatedmetallic tape, as shown, for example, by the cross section of conductor60′ in FIG. 5b. Furthermore, rather than weld portions 77 and 79 ofsheet 75 to one another on the side of composite ceramic tape 62, as inFIGS. 5a and 5 b, portions 77 and 79 can be welded to one another on thetop of composite ceramic tape 62 as shown for conductor 60′′ in FIG. 5c.

In preferred embodiments, the ductile sheet is conductive so that whenmultiple conductors 60 are stacked on top of one another there arecurrent pathways between adjacent conductors. Suitable materials for theductile sheet are copper, copper alloys, stainless steel andsuperalloys. Suitable thicknesses for the ductile sheet are comparableto those described above for the metallic tapes. The sheet can bewrapped around the composite ceramic tape or laminated structure by rollforming. See, e.g., Handbook of Metal Forming Processes, eds., Betzaleland Avitzur (Wiley Publishing, 1983), section 9.2.1, pg. 459.

In further embodiments, the sealing structure can be a curable polymermaterial, e.g., an acrylate polymer, which is applied to the top,bottom, and sides of a composite ceramic tape or laminated ceramic andmetallic tapes and cured to hermetically seal the conductor from thefluid cryogen. For example, referring to FIG. 6, a conductor 310includes a superconducting composite ceramic tape 312 having a metallictape 316 laminated to top surface 320 a by solder layer 314. Compositeceramic tape 312 and laminated metallic tape 316 are similar to thosedescribed above, with metallic tape 316 imparting mechanical strength tocomposite ceramic tape 312. In further embodiments, a second metallictape can be laminated to the bottom face of the ceramic tape to providefurther mechanical reinforcement. Cured polymer layer 375 surrounds thetop, bottom, and sides of laminated tapes 312 and 316 and extends alongtheir length to hermetically seal the conductor from fluid cryogen 330.The polymer layer can be applied to the laminated ceramic and metallictapes by coating or dipping and can then be cured thermally or byexposure to UV radiation. Suitable curable polymers include theDesolite® 2002-17 family from Desotech (Elgin, Ill.), which are UVcurable acrylate polymers. This family of polymers has superiormechanical properties at cryogenic temperatures. For example, at 77 K,the ultimate tensile strength (UTS) is at least about 100-160 MPa andthe elongation is at least about 0.3% to 0.5%.

Preferably, the polymer layer would be applied to laminated tapes 312and 316 in an in-line fashion immediately following lamination. Forexample, referring to FIG. 7, the laminated tapes 400 are drawn througha die 402 into a bath 404 containing uncured polymer 406 under anitrogen purge 408. Polymer 406 coats tape 400, which is then drawnthrough a second die 412. The coated tape is then exposed to ultravioletlight from UV source 414 to cure the polymer and form polymer layer 416.

Referring again to FIG. 6, in some embodiments, conductive media 380such as copper, silver, gold, or aluminum particles (having, e.g.,diameters of about 10-20 microns) are dispersed within polymer layer 375so that the cured polymer-sealed conductor is also conductive along atleast its thickness (i.e., along the z-axis). Conductivity along thethickness provides an alternative current path in applications such aspower cabling in which many superconducting .ceramic conductors arestacked on top of one another and where current transfer between layersmay be important. In such applications, the conductive media is added toand dispersed within the polymer prior to coating the laminated tapes.The amount of conductive media within the polymer is sufficient toimpart the desired conductivity along the z-axis. The conductive mediacan also include metallic rods or screens. For example, the polymercoating could encapsulate a conductive wire mesh.

FIG. 9 shows a system 250 including a superconducting article 260 suchas a cable utilizing a conductor 10 made in accordance with theinvention. The embodiment illustrated in FIG. 9 allows cryogen 251 toact as a heat transfer medium in system 250. In particular, cryogen 251is contained in vessel 252 which also contains a superconducting article260 comprising conductor 10, which may be, for example, asuperconducting cable viewed in cross section or a superconductingmagnet coil. Superconducting article 260 is at least partially immersedin the fluid cryogen 251 with the conductor 10 in direct contact withthe fluid cryogen 251. The temperature of cryogen 251 is maintainedwithin a desired range, e.g., liquid nitrogen temperatures, bycirculating cryogen 251 through refrigeration unit 254 and circulatingpump 258 in line 256. While not to be construed as limiting, the fluidcryogen 251 could be, for example, liquid nitrogen, liquid helium,liquid hydrogen, or supercritical helium. The temperature of the fluidcryogen 251 in line 256 is maintained by refrigeration unit 254. Theamount of material in article 260 determines the load on the unit 254,and thus the operating cost of the assembly 250.

By using the sealing structures described above for protection againstcryogen 251 infiltration of the composite ceramic tape 12, the thicknessof the matrix material 40 in the composite ceramic tape 12 can typicallybe substantially reduced or the fill factor of the superconducting tapecan be increased. Absent the sealing structure as provided by thepresent invention, increasing the fill factor reduces the externalthickness of the composite material and thereby increases the likelihoodof surface defects that give rise to balloons. Moreover, obtaininglarger fill factors typically requires more severe manufacturingconditions that also increase the likelihood of surface defects thatcould give rise to balloons absent the sealing structure. Thus thesealing structure permits an increase in fill factor and a correspondingincrease in critical current density without increasing the likelihoodof balloon formation. This is a particularly significant advantage forlong length cables because it reduces the number of tapes needed for acable and also reduces operating costs. It can also a significantconsideration for any application in which the superconducting articleis placed in a pool-boiling fluid cryogen environment where the articleis directly cooled by the fluid cryogen.

Typical operation conditions for the superconducting article 260 includetemperatures of 66 to 80 K, and, for pressurized environments, pressuresof about 1 to 33 atm, e.g., about 10-15 atm. Circulating pump 258 can beused to create such pressures. In some applications, article 260 can beexposed to such conditions for many years. However, article 260 mustalso withstand thermal cycling in which the article is returned toambient conditions for, e.g., normal servicing. The sealing structuresdescribed above minimize degradation of the superconducting articlecaused by cryogen infiltration despite such operating conditions andthermal cycling.

The invention may be further understood from the following non-limiitingexamples.

EXAMPLE 1

A BSSCO multifilament composite ceramic tape was laminated usingoverhanging stainless steel metallic tapes as described above. Themetallic tapes were 0.154″ wide and the composite ceramic tape was0.124″ wide. Solder fillets were approximately 0.015″ (along the widthor x-direction) on each side of the composite ceramic tape. Thelamination process used to insure continuous fillets included a preheattemperature prior to soldering in excess of 100° C., positive pressure(5-10 MPa) on the laminated tapes as they exit the solder pot, and rapidsolidification with air knifes. The ends of the conductor wereseparately sealed using a silicon, in particular, Dow Corning 732multi-purpose sealant available from Dow Corning Corporation (Midland,Mich.). Sample conductors were soaked in liquid nitrogen for up to sixweeks at ambient pressure. After being returned to ambient conditions,no balloons were apparent. In another test sequence, sample conductorswere aged at 125° C. for up to 72 hours and then soaked in liquidnitrogen at 10 atm for up to 36 hours. After being returned to ambientconditions, no balloons were apparent. Wire lengths for both testsequences were about 5-15 meters.

EXAMPLE 2

BSSCO multifilament composite ceramic tapes were laminated withstainless steel metallic tapes on their top and bottom faces. Thecomposite ceramic tapes were approximately 0.160″ wide and the metallictapes were approximately 0.154″ wide, so that the metallic tapes did notoverhang the composite tape. The laminated tapes were then coated withan acrylate coating and UV cured. Sample conductors were then thermallycycled ten times from 77 K to room temperature over eight hours, andthen soaked in liquid nitrogen for two weeks under ambient pressure.After being returned to ambient conditions, no balloons were apparent.In a second test, sample conductors were thermally cycled ten times from77 K to room temperature and then soaked in liquid nitrogen for 36 hoursat 10 atm. After being returned to ambient conditions, no balloons wereapparent.

EXAMPLE 3

A first set of BSSCO multifilament composite ceramic tapes werelaminated with stainless steel metallic tapes on their top and bottomfaces using a solder lamination process without overhanging metallictapes. The stainless steel tapes were about 0.153″ wide and coveredabout 95% of the top and bottom surfaces of the composite ceramic tapes,which were about 0.161″ wide.

A second set of BSSCO multifilament composite ceramic tapes were alsolaminated with overhanging stainless steel metallic tapes on their topand bottom faces using the solder lamination process described above andin Example 1. In the second set, the stainless steel tapes were about0.197″ wide, which was wider than the composite ceramic tapes, whichwere about 0.153″ wide.

Both sets of samples were soaked in liquid nitrogen at 30 atm for 16hours after their ends were sealed with separate solder caps. Uponremoving the samples from the liquid nitrogen bath, all of the samplesfrom the first set had balloon formation, whereas none of the samplesfrom the second set had balloon formation.

EXAMPLE 4

Two sets of BSSCO multifilament conductors were manufactured as inExample 3. The samples were mechanically aged by applying aunidirectional pressure over the conductor surface to simulate thecryostat effect present in a power transmission cable application. Afterthe mechanical aging, the samples were soaked in liquid nitrogen at 5bar for 8 hours. Upon removing the samples from the liquid nitrogenbath, all of the samples from the first set had balloon formation,whereas none of the samples from the second set had balloon formation.

EXAMPLE 5

Two sets of BSSCO multifilament conductors were manufactured as inExample 3. The samples were mechanically aged by applying bending,tensile and torsion deformations to simulate the deformation appliedduring the manufacturing phase of a power transmission application(e.g., a cable transformer). No degradation of the conductors' criticalcurrent density was observed following the mechanical aging. After themechanical aging, the samples were soaked in liquid nitrogen at 30 barfor 16 hours. Upon removing the samples from the liquid nitrogen bath,all of the samples from the first set had balloon formation, whereasnone of the samples from the second set had balloon formation.

EXAMPLE 6

Two sets of BSSCO multifilament conductors were manufactured as inExample 3 and mechanically aged as in Example 5. The samples were thenfurther mechanically aged by winding them on an aluminum cylindricalmandrel having a coefficient of thermal expansion greater than that ofthe conductors and heating them to more than 100° C. for about 100hours. The wound conductors were then fast cycled (i.e., until the bathreaches equilibrium) tens times between a liquid nitrogen bath at 1 atmand room temperature. The conductors were,then placed in a liquidnitrogen bath at 30 bar for 16 hours. Upon removing the samples from theliquid nitrogen bath, all of the samples from the first set had balloonformation, whereas none of the samples from the second set had balloonformation. Similar results were obtained when the order of themechanical and thermal aging processes were reversed.

Other aspects, advantages, and modifications are within the scope of thefollowing claims. For example, although the detailed description abovereferred to composite ceramic superconducting tapes, which havesubstantially rectangular cross sections, more generally, the sealingstructure can hermetically seal composite ceramic superconducting wires(such as tapes or rods) having arbitrary cross sections, e.g., circular,elliptical, or rectangular cross sections.

What is claimed is:
 1. A superconducting article, comprising: a ceramicsuperconductor in the form of a superconducting tape, the ceramicsuperconductor having a length and an outer surface along its length;and a sealing structure comprising a cured polymer layer encircling theouter surface of the ceramic superconductor, the cured polymer layerbeing configured to form a seal to prevent a cryogenic fluid at apressure of about one atmosphere from infiltrating into the ceramicsuperconductor through the outer surface of the ceramic superconductor,wherein the superconducting article is in the form of a cable.
 2. Thearticle of claim 1 further comprising a metallic layer laminated to theceramic superconductor, the cured polymer layer surrounding the metalliclayer.
 3. The article of claim 1, wherein the cured polymer layercomprises a metallic electrically conductive medium.
 4. The article ofclaim 3, wherein the metallic electrically conductive medium comprisesmetallic elements disperse within the polymer layer.
 5. The article ofclaim 3, wherein the ceramic superconductor is in the form of a tapehaving a thickness and wherein the electrically conductive mediumpermits the cured polymer layer to be conductive at least along adirection parallel to the thickness of the tape.
 6. The article claim 1,wherein the article is greater than 50 meters long.
 7. The article ofclaim 1, wherein the ceramic superconductor comprises a plurality ofsuperconducting ceramic filament, and the article further comprises ametallic matrix supporting the plurality of superconducting ceramicfilaments.
 8. The article of claim 1, wherein the ceramic superconductorcomprises at least one superconducting ceramic layer, and the articlefurther comprises at least one metallic substrate supporting the atleast one superconducting ceramic layer.
 9. The article of claim 1,wherein the seal formed by the cured polymer layer prevents a ceramicfluid at a pressure of at least about two bar from infiltrating into theceramic superconductor through the outer surface of the ceramicsuperconductor.
 10. The article of claim 9, wherein the seal formed bythe cured polymer layer prevents a cryogenic fluid at a pressure of atleast about 10 atmospheres from infiltrating into the ceramicsuperconductor through the outer surface of the ceramic superconductor.11. The article of claim 1, wherein the cured polymer layer has anultimate tensile strength of at least about 100-160 MPa at 77 K.
 12. Thearticle of claim 1, wherein the cured polymer layer has an elongation ofat least about 0.3% to 0.5% at 77 K.
 13. The article of claim 1, whereinthe cured polymer layer has an ultimate tensile strength of at leastabout 100-160 Mp at 77 K and an elongation of at least about 0.3% to0.5% at 77 K.
 14. The article of claim 2, wherein the article furthercomprises a metallic layer between the cured polymer layer and theceramic superconductor.
 15. A superconducting article, comprising: aceramic superconductor in the form of a superconducting tape, theceramic superconductor having a length and an outer surface along itslength; and a sealing structure comprising a cured polymer layer that isapplied to the outer surface of the ceramic superconductor to form aseal that permits the article to withstand thermal cycling when exposedto a fluid cryogen at a pressure of at least about one atmospherewithout degrading the current carrying capability of the ceramicsuperconductor by more than 10%. wherein the superconducting article isin the form of a cable.
 16. The article of claim 15, wherein the sealingstructure is configured to permit the article to withstand thermalcycling when exposed to a fluid cryogen at a pressure of at least abouttwo bar without degrading the current carrying capability of the ceramicsuperconductor by more than 10%.
 17. The article of claim 15, whereinthe seal formed by the cured polymer prevents a cryogenic fluid at apressure of at least about two bar from infiltrating into the ceramicsuperconductor through the surface of the ceramic superconductor. 18.The article of claim 15, wherein the seal formed by the cured polymerprevents a cryogenic fluid at a pressure of at least about 10atmospheres from infiltrating into the ceramic superconductor throughthe outer surface of the ceramic superconductor.
 19. The article ofclaim 15, wherein the cured polymer layer comprises an electricallyconductive medium.
 20. The article of claim 19, wherein the electricallyconductive medium comprises metallic elements dispersed within thepolymer layer.
 21. The article of claim 15, wherein the article furthercomprises a metallic layer between the cured polymer layer and theceramic superconductor.